An idealized example of the OUR response for a wastewater sample using an activated sludge containing nitrifying bacteria is shown on Fig 7-4. The OUR versus time can be divided into four areas, which can be used to determine the oxygen consumed for the reaction indicated by the area. Area A is the oxygen used for rbCod degradation area nitrification, area C for particulate COD degradation. and area COD angen demand Nitrogen Compounds. For the nitrogen compounds, the soluble organic nitrogen concentration is of interest fre 0 fect on the effluent total nitrogen concentration. A filtered sample from the plant effluent or from a bench-scale treatability reactor can be used to determine the total effluent soluble organic nitrogen concentration by the difference between the tKn concentration of the filtered sample and the effluent NH4-N concentration Recycle flows and loadings The impact of recycle flows must also be quantified and included in defining the influent wastewater characteristics to the activated-sludge process. The possible sources of recycle flows include digester supernatant flows(if settling and decanting are practiced in the digestion operation), recycle of centrate or filtrate from solids dewatering equipment, backwash water from effluent filtration processes, and water from odor-control scrubbers. Depending on the source, a significant BOD, TSS, and NH4-N load may be added to the influent wastewater. Compared to untreated wastewater or primary clarifier effluent, the BOD/VSS ratio is often much lower for recycle streams. In addition, a significant NH-N load can be returned to the influent wastewater from anaerobic digestion-related processes. Concentrations of NH4-N in the range of 1000 to 2000 mg/L are possible in centrate or filtrate from the dewatering of anaerobically digested solids. Thus, the ammonia load from a return flow of about one-half percent of the influent flow can increase the influent TKN load to the activated-sludge process by 10 to 20 percent. The return solids load from effluent polishing filters can be estimated by a mass balance on solids removed across the filtration process, and thus released in the backwash water flow. In all cases, a mass balance for flow and mport fo constituents, inc haws ond ads to the nitrogse -s mpoe nds end phosphorus should be done to 7-3 Fundamentals of Process Analysis and Control The purpose of this section is to introduce (1) the basic considerations involved in process design, (2) process control measures, (3)operating problems associated with the activated-sludge process, and (4) activated-sludge selector processes Process Design Considerations In the design of the activated-sludge process, consideration must be given to(I) selection of the reactor type,(2)applicable kinetic relationships, (3)solids retention time and loading criteria to be used,(4) sludge production, (5)oxygen requirements and transfer, (6) nutrient requirements, (7)other chemical requirements, 8)settling characteristics of biosolids, (9)use of selectors, and (10)effluent characteristics Selection of Reactor Type. Important factors that must be considered in the selection of reactor types for the activated-sludge process include(1) the effects of reaction kinetics, (2) oxygen transfer requirements, (3)nature of the wastewater, (4)local environmental conditions, (5) presence of toxic or inhibitory substances in the influent wastewater,(6)costs, and(7)expansion to meet future treatment Selection of Solids Retention Time and Loading Criteria. Certain design and operating parameters e process from another. The common parameters used are the solids retention time(SRD), the food to biomass(F/M)ratio(also known as food to microorganism ratio), and the volumetric organic loading rate. While the Srt is the basic design and operating parameter, the F/M ratio and volumetric loading rate provide values that are useful for comparison to historical data and typical observed operating conditions Solids Retention Time. The SRT, in effect, represents the average period of time during which the7-5 An idealized example of the OUR response for a wastewater sample using an activated sludge containing nitrifying bacteria is shown on Fig. 7-4. The OUR versus time can be divided into four areas, which can be used to determine the oxygen consumed for the reaction indicated by the area. Area A is the oxygen used for rbCOD degradation, area B for zero-order nitrification, area C for particulate COD degradation, and area D for endogenous decay Nitrogen Compounds. For the nitrogen compounds, the soluble organic nitrogen concentration is of interest from the standpoint of its effect on the effluent total nitrogen concentration. A filtered sample from the plant effluent or from a bench-scale treatability reactor can be used to determine the total effluent soluble organic nitrogen concentration by the difference between the TKN concentration of the filtered sample and the effluent NH4-N concentration. Recycle Flows and Loadings The impact of recycle flows must also be quantified and included in defining the influent wastewater characteristics to the activated-sludge process. The possible sources of recycle flows include digester supernatant flows (if settling and decanting are practiced in the digestion operation), recycle of centrate or filtrate from solids dewatering equipment, backwash water from effluent filtration processes, and water from odor-control scrubbers. Depending on the source, a significant BOD, TSS, and NH4-N load may be added to the influent wastewater. Compared to untreated wastewater or primary clarifier effluent, the BOD/VSS ratio is often much lower for recycle streams. In addition, a significant NH4-N load can be returned to the influent wastewater from anaerobic digestion-related processes. Concentrations of NH4-N in the range of 1000 to 2000 mg/L are possible in centrate or filtrate from the dewatering of anaerobically digested solids. Thus, the ammonia load from a return flow of about one-half percent of the influent flow can increase the influent TKN load to the activated-sludge process by 10 to 20 percent. The return solids load from effluent polishing filters can be estimated by a mass balance on solids removed across the filtration process, and thus released in the backwash water flow. In all cases, a mass balance for flow and important constituents, such as BOD, TSS/VSS, nitrogen compounds, and phosphorus should be done to account for all contributing flows and loads to the activated-sludge process. 7-3 Fundamentals of Process Analysis and Control The purpose of this section is to introduce (1) the basic considerations involved in process design, (2) process control measures, (3) operating problems associated with the activated-sludge process, and (4) activated-sludge selector processes. Process Design Considerations In the design of the activated-sludge process, consideration must be given to (1) selection of the reactor type, (2) applicable kinetic relationships, (3) solids retention time and loading criteria to be used, (4) sludge production, (5) oxygen requirements and transfer, (6) nutrient requirements, (7) other chemical requirements, (8) settling characteristics of biosolids, (9) use of selectors, and (10) effluent characteristics. Selection of Reactor Type. Important factors that must be considered in the selection of reactor types for the activated-sludge process include (1) the effects of reaction kinetics, (2) oxygen transfer requirements, (3) nature of the wastewater, (4) local environmental conditions, (5) presence of toxic or inhibitory substances in the influent wastewater, (6) costs, and (7) expansion to meet future treatment needs. Selection of Solids Retention Time and Loading Criteria. Certain design and operating parameters distinguish one activated-sludge process from another. The common parameters used are the solids retention time (SRT), the food to biomass (F/M) ratio (also known as food to microorganism ratio), and the volumetric organic loading rate. While the SRT is the basic design and operating parameter, the F/M ratio and volumetric loading rate provide values that are useful for comparison to historical data and typical observed operating conditions. Solids Retention Time. The SRT, in effect, represents the average period of time during which the Fig. 7-4 Idealized oxygen uptake rate(OUR) in aerobic batch test for a mixture of influent wastewater and activated-sludge mixed liquor. Area A represents rb COD oxygen demand